An image forming apparatus which employs an electrophotographic system mainly includes an electrophotographic photosensitive member, a charging device, an exposure device, a developing device, a transfer device, a cleaning device, and a fixing device. The charging device employs a system in which a surface of the electrophotographic photosensitive member (hereafter also referred to as “a photosensitive member”) is charged by applying a voltage (direct voltage or voltage obtained by superimposing alternating voltage on direct voltage) to a charging member which contacts or is closely disposed on the surface of the photosensitive member. A contact-type charging method is preferably used in order to stably perform charging and reduce the amount of ozone generated. In the case of the contact-type charging method, a roller-shaped charging member is preferably used.
In recent years, high speed, high image quality, high durability, and downsizing have been required for image forming apparatuses. To achieve this, PTL 1 or 2 discloses a technique of forming a surface layer having projections on a surface of a charging member, the projections being derived from resin particles or the like. In this technique, the uniform chargeability is believed to be improved by performing in-nip discharge near the projections as described in PTL 3. This can suppress the generation of images of lateral streaks formed due to nonuniformity of electrical resistance (hereafter referred to as “lateral streak images”).
However, if such projections derived from resin particles are formed on the surface layer as described above in a trend of increasing the speed, image quality, and durability and decreasing the size, the photosensitive member tends to contact only the top portions of the projections. Therefore, the contact area is small and the contact pressure is concentrated, which sometimes causes slippage between the charging member and the photosensitive member. In the case where a toner (hereafter also referred to as “a residual toner”) left on the surface of the photosensitive member after a transfer step is not removed in a cleaning step, the unremoved toner is rubbed in the sliding between the photosensitive member and the charging member due to the slippage of the charging member and thus is fixed on the surface of the charging member. The fixation of the toner degrades the discharge performance of the charging member. As a result, the lateral streak images and spot-like images formed by abnormal discharge in toner-fixed portions (hereafter referred to as “spot-like images”) are easily generated. The solution to this problem is not described in PTL 1 or 2.